BME 474 Exam 1

Biomaterial

nonviable (nonliving) material that interacts with biological systems (synthetic or natural)

Biocompatibility

ability of a material to perform an appropriate host response for that application

Needs FDA approval if it ______

diagnoses, cures, or treats

FDA medical device classes

low risk (bandaids), medium risk (ear tube), high risk (invasive surgery)

Verification vs validation

verification: verifying/testing if device meets specification (design input & output)

validation: testing if device needs user needs

Commercialization depends on _____

number of patients, risk/benefit, cost, market size

Hydroxyl group

polar (charged) -OH groups, hydrophillic

Carboxyl group

polar, hydrophillic, R-OOH

Amino group

functional group (R), R-NH_2

Stress

F/cross-sectional area, "strength"

Strain

deformation/length

Setup for stress-strain testing

strain on x-axis, stress on y-axis; change in stress w/ material being deformed at constant rate of strain

Engineering vs true stress-strain

engineering/nominal: area & length are constant

true: area & length are variable

Biomedical properties that cannot be found on single stress-strain curve

viscoelasticity, anisotropy, and hardness

Mechanical properties in stress-strain curve

Young's Modulus (stiffness), yield strength (point of permanent deformation), ultimate tensile strength (maximum load-bearing capacity), and toughness (energy absorption before fracture); distingusihes between ductile and brittle materials

High vs low surface energy

High: spreading adhesive forces

Low: stronger cohesive forces (more bubble shape)

Contact angle analysis pros and cons

pros: simplicity, direct indication of surface wettability and energy

cons: sensitivity to surface roughness and contamination, the need for a large liquid volume, potential contamination of samples

Electron Spectroscopy

interactions with electron beams to determine surface properties

Secondary Ion Mass Spectrometry (SIMS)

vacuum, using positive ions to eject positive/negative ions from surface; tells us more about functional groups

Scanning Electron Microscope (SEM)

high resolution image of surface, in vacuum

Atomic Force Microscopy (AFM)

not a vacuum, sub nanometer resolution that shows surface geometry & molecular interactions

Spectrometry

observing chemical composition

Microscopy

observing surface roughness/geometry

General polymer structure

large number of similar units bounded together, monomers held together by covalent bonds to form polymer

Hydrogel

polymers designed to expand with water, very hydrophillic; gel to solid through cross-linking; useful for drug delivery, wound repair, tissue engineering

Degradable polymers

enzymes, acids, cells in body; PLA, PGA, PLGA

In vivo

in living system

In vitro

on lab bench; mechanical systems

In situ

at the site-with blood

Ex vivo

implanted device, then remove impact & surrounding tissue

In silico

computational modeling

FDA Class I

low risk, does not require premarket notification

FDA Class II

medium risk, requires premarket notification, 510K

FDA Class III

high risk, requires premarket approval (PMA), animal & patient testing, and investigated device exemption

510k

can get approval through a similar different FDA approved device

Title 21 of the Code of Federal Regulations (CFR)

guide to how to get FDA approval

Good Laboratory Practice (GLP)

good lab practices, very documented (FDA->IDE->clinical testing)

Van der waals forces

weak, dispersion forces, polymer chains

Ionic forces

very strong, positive & negative charge atoms, rigid/crystal structure

Hydrogen bonding

water, polarity

Metallic forces

metals, positively charged ions in sea of delocalized electrons

Covalent interactions

shared electron between 2 atoms, very strong

Collagen

structural protein in all tissues of body; hierarchical structure; one chain is weak, adding more chains makes it stronger

Primary structure

amino acids in sequence, polypeptide chain

Secondary structure

alpha helix & beta pleated sheets

Tertiary structure

general 3D structure

Quaternary structure

subunits (eg. hemoglobin), most stable, protein shape is dynamic

Amino acid

building block for proteins, containing both a carboxyl (—COOH) and an amino (—NH2) group.

Polar vs non-polar

polar: charged & hydrophillic

nonpolar: uncharged & hydrophobic

Amino acid side chain

R-group, varies with each amino acid; helps to make 3D shape

Polymers

plastic; molecular structure consisting of large number of similar units bounded together

Metals

positive ions in sea of electrons; high ultimate strength, useful for orthopaedics

Ceramics and glasses

Polycrystalline, nonmetallic w/ oxide, nitride, inert (rigid, high order)

Bulk properties

mechanical properties

Surface properties

properties of a material associated with its surface

Linear vs nonlinear properties

Linear: higher crystallinity, line of monomers

Nonlinear: low crystallinity, more branched

Elastic vs plastic properties

elastic: can go back to original shape, weak forces with van der waals and hydrogen bonding

plastic: deformation permanent

Proportionality limit

where linear relationship between stress and strain ends

Elastic limit

deformation is reversible; maximum stress a material can withstand without permanent (plastic) deformation, even if the stress-strain relationship is no longer linear (slightly past proportionality limit)

Yield strength

yielding (elongation)-occurs w/o changing load, past yield stress will not go back to original shape

Ultimate strength

highest point of strength/stress on graph

Rupture strength

the stress at which a material physically breaks or fractures under load

Elastic/Young's Modulus (E)

slope of linear region, rigidity of material

Ductility

brittleness, percent of elongation

Toughness

area under ENTIRE curve

Resilience

area under elastic/linear region; ability of material to absorb energy w/o plastic (permanent) deformation

Homogeneity

material properties vary by location within a material

Isotropic vs anisotropic

isotropic: will deform the same way wherever you apply load

anisotropic: only made for applied load up & down, NOT side-to-side (low ultimate strength axially)

Poisson's ratio

(lateral/axial) strain; measures the Poisson effect—the deformation of a material perpendicular to the direction of applied load

Strain rate

constant, load applied to materials while testing it, variable control in testing

Viscoelasticity

biological, material's behavior is time dependent, strain rate dependent

Hardness

measures a material's resistance to permanent deformation from indentation, scratching, abrasion, or cutting, cannot measure on stress-strain curve

Fracture toughness

crack in material-> how material resists failure/the propagation of crack

Fatigue

multiple loading cycles, can use failure earlier (use smaller loads for testing)

Contact angle analysis

measures wetability, cheapest method, cohesive (rounded droplet) vs. adhesive forces (spreading of droplet); testing multiple liquids w/ known γ_lv (surface tension), tells us about surface tension and how material will interact with body

Surface energy

degree of attraction/repulsion force from a substrate to another material

Critical surface tension

complete wetting, θ=0; compare to known materials

Zisman Plot

γ_lv on x-axis, contact angle θ b/n droplet and material on y-axis; trying to predict γ_sv

Branched polymer

a long polymer chain with shorter chains (branches) attached to a main backbone, creating a tree-like structure; reduce crystallinity

Cross-linking

chemical or physical bonds that connect individual polymer chains, creating a network structure; adding covalent bonds->increase in rigidity, NOT affected by Tg or Tm bc they cannot break covalent bonds

Copolymer

less crystallinity; a polymer formed from two or more different monomers covalently bonded into a single polymer chain

Polymer pendant groups

atoms or smaller chains that "hang off" the main backbone of a polymer; smaller pendant groups = higher crystallinity

Tacticity

stereochemistry of the monomers in polymer chain (3D orientation); orientation of pendant groups, affects how polymers interact & crystallinity

Isotatic

same orientation for repeating unit

Syndiotactic

alternating unit

Atactic

random orientation

Molecular weight

length of polymer chains; calculating avg. molecular weight is important to find PDI

Degree of polymerization (DP)

number of monomers/repeating units

Polydispersity index (PSI)

(weight avg. molecular weight/number avg. molecular weight), molecular mass distribution; is there a lot of variation? closer to 1->wide variation

Amorphous structure

disorganized, random, atactic (rubbery, flexible, lower modulus & Tg)

Crystalline structure

highly organized, rigid (strong), polymer chains are "zipped-up" and align perfectly

Glass transition temperature (Tg)

glassy (brittle) state->rubbery (flexible) state; breaks weak bonds & interactions b/n chains

Melt temperature (Tm)

melt crystalline; add/remove interactions b/n polymer chains; higher Tm=higher crystallinity

Semi-crystalline state

polymers are co-aligned, "zipped-up", organized, isotactic, syndiotech (glassy, more rigid, less change w/Tg, Tm)

Biostable

a material that resists negative changes to its properties when exposed to the biological environment

Biodegradable

breaking down with water; enzymes, acids, cells in body

Hydrolysis

backbone breakdown with water

Addition polymerization

biostable; initial bond(initiation)->second bond(propagation), termination (2 free radicals combine)

316L stainless steel

alloy of Fe, Cr, Ni, Si, C

pros: cheap, easy to shape, fatigue resistant

cons: long term corrosion, Ni & Cr allergies

use: temporary implants

Chromium (Cr)

hard, lustrous, silver-gray metal that is highly resistant to corrosion and tarnishing due to a protective oxide layer it forms in air